The Relation BetweeG Solar Cell Flight Performance Data and Materials and Manufacturing Data Report No. 3 Third Quarterly Report Contract No. NASW-1732 Prepared by The CARA Corporation 101 N. 33rd Street Philadelphia, Pennsylvania ’S. R. Pollack, Ph.D. G. R. Zin, P’h.D. Principal Investigator L. A. Girifalco, Ph.D. Staff Scientists ABS TRACT This quarter was spent in acquiring data for the flights chosen for study in the last quarter. Analysis of the environment for the individual flights has begun. This work is progressing with the viewpoint of trying to simplify the environmental specification. The most difficult aspect of the environmental analysis is the speci- fication of the vehicle's thermal history. The vehicles under study are therefore being grouped according to subclassifica- tions based on the nature of the vehicle as the first attempt to find any performance correlations. All of the specific data for the flights under study have been extracted from the literature obtained from the computer searches conducted earlier. These data are incomplete and in- adequate for this study. Examples of the nature of this data were reported in the last quarterly,report and are shown in 8 this report. The data required for this study must be obtained by personal contacts with individuals who have been connected with the various flights. The appropriate individuals to contact have been identified for 75 of the 77 flights included in this study. These people have been and are being contacted to obtain the required data. i Table of Contents Fage I. Introduction 1 11. The Selected Flights and Environment 3 111. Information and Data Gathering 11 IV. Summary 19 List of Tables Page Table I. Orbital Integration Flux Versus Orbital Parameters 4 Table 11. Specific Flights to be Studied 8 Table 111. Specific Flights with Individual Contact 14 Appendix I. Form C-03, Outline for Recording Pertinent Data, (Ariel 3) 20 I. Introduction This document is the third quarterly report in a program to examine the flight performance data for. solar cell power systems in satellites, and to try to relate the differences in performance to the materials and manufacturing factors in the solar cell system. The general method of approach Gonsists of selecting a group of flights whose space environments are all similar, for which sufficient flight performance data exists, and for which information on the materials and manufacturing factors is available. For the selected group of flights, an attempt will be made to relate the differences in per- formance to specific materials or manufacturing parameters that may be expected to affect performance. The work is divided into four general phases defined by the following outline: Phase I: A. Classify a11 flights from 1957 through 1967 accord- ing to their space environment, so that groups of flights with similar environment can be identified. B. Ascertain availability of performance data and ma- terials and manufacturing parameters. C. Generate a coding procedure to facilitate the re- cording and use of information gathered relative to performance and materials and manufacturing factors. Phase IT: Select a group of flights based on the work in Phase I. Phase 111: Acquire and systematize the actual data needed for the flights selected in Phase 11. Phase IV: Perform analysis to relate materials and manu- facturing factors to flighe performance of the selected flights. Phase I and Phase 11 have been completed and work has begun on Phase 111. This past quarter was spent in extract- ing and organizing the information contained in the liter- ature obtained in our literature search. Visits were made to determine where and in what form the information required by this study exists. It has been determined that the data required for the performance of this contract are contained in documents which do not receive wide distribution. These documents can only be acquired through personal contacts; the flights to be studied and the,people associated with 3 them have been organized so that the required information can be obtained. Information of this nature has been re- quested, and ob.tained for several flights and is being ana- lyzed so that the remaining flights may be documented in as efficient a manner as possible. The rest of the data re- quired for this study will be requested and obtained in the next quarter. At the end of the next quarter, Phase IV, the analysis and correlation phase will begin. 2 11. The Selected Flights and Environment As was reported in the first quarterly report, an exam- 'ination of the Space Projects Log from 1957 to 1968 yielded approximately 611 earth satellite flights. By applying the conditions that a suitable flight for study under this con- tract be (a) in orbit and transmitting data for three months or more, (b) have NASA or DOD as the Project Director, and (c) be unclassified, the number of flights suitable for study were reduced to slightly over 200. These flights were listed in the first quarterly report. A plot of perigee vs. apogee for these flights showed a number of clusters along the 45' line, suggesting that a rational starting point for selecting flights with similar environments could be chosen by defining four major sets of orbits. I (inside orbit) orbits were defined as having peri- gee and apogee just inside the first radiation belt. The cutoff point for orbit parameters was arbitrarily chosen to \ be 760 miles, because above this altitude both electron and proton fluxes increase very rapidly with altitude from negli- gible to quite significant values. The B (first belt orbit) orbits were defined to be the cluster of flights with perigee and apogee at about 2,000 miles, which is close to the maximum ' of the first radiation belt, The S (synchronous orbit) orbits, with parameters around 20,000 miles, are the synchronous geo- stationary flights, and the 0 (outside orbit) orbits, with orbit parameters between 60,000 and 70,000 miles, are beyond the radiation belts. The I' orbit flights were chosen to be the subject of this study. These flights can be divided into four sub- groupings; thirteen flights with angle of inclination be- tween 28O and 33O; sixteen flights with angle of inclination 3 between 47O and 60'; nineteen flights with angle of incli- 0 nation between 66O and 71 ; and twenty-nine flights with 0 0 angle of inclination between 79 and 135 The I orbit flights suffer minimal radiation damage since.they are below the maxima in the first radiation belt. However, because of the low orbit, the thermal cycle has appreciable changes in temperature over times measured in minutes. A review of the literature indicates that much more work has been done in examining the radiation effects on solar cells than on any other effect , An indication of the variability of the radiation environ- ment is given in Table I which gives approximate values for the orbital integration flux for protons and electrons of energies greater than 4 M.eV and 0.5 MeV respectively for several orbits 2 -1 in units of (cm -day) . 0 0 8=0 e = 30 Table I Orbital Integration Flux Versus Orbital Parameters This table shows that there is a considerable variation in the radiation environment, even though the level is much lower than in the Van Allen belt. A theoretical calculation of the effect of radiation at -9.. 300 NOM, (Cooley and Barret)" indicates that the radiation field -1- A W. C. Cooley & M, J. Barrett, Space Environmental Effects in Solar Cell. Power Systems, January 1968, (Exotech Report TR-025) will cause 7% degradation in maximum power in a typical solar cell array in one year, while test data for Anna lB, with an orbit in the 700 mile region, indicated degradations in short circuit current after 400 days ranging from 10% to 45% de- pending on the cover glass thickness. There are several conclusions of importance to this study that arise from an examination of the near earth radiation environment. The first is that for orbits above approximate 250 N.M., the radiation effects may still be serious, while below this region, they are less important. This, coupled with the variability of the radiation density with altitude and epoch, means that orbital integrated fluxes must be ob- tained for each of the €lights chosen for study. It is clear that the coarse grained classification of environment based on four orbital parameters is insufficient for the purposes of our study. However, it may still be true that the angle of inclination is an adequate representation of the orienta- tion of the orbital plane. This' is' true to the extent that the radiation flux is symmetrical with respect to the orbital plane. For those flights for which the radiation effects are severe, however, the existence of variations in the radiation symmetry (such as those arising from the South Atlantic Anomdly) will require use of the orbital angular parameters completely defining the orientation of the orbital plane relative to the equatorial plane. Because of this, and because of secular variations, it will probably become necessary to use orbital integrated fluxes for each flight as the appropriate radia- tion environmental parameters. The available data on the meteoroid environment has been ,r, summarized by Lyle in a report by Cooley and Barrettn. From 5 the data given in their report, a rough representation of the 2 near earth meteoroid flux in (m - set)-' for particles of mass greater than lom8gms, is 1.15 IO-^(^-^) JM = e where R is the altitude in kilometers. Thus, the meteoroid flux, within the accuracy of the avai-lable data, is essentially constant for all the inside orbits of this study.